when running the driver test... with nothing else on... i get 45000

when I run it with Mach3 on and powered up... just minimized... I get 25000

Do I set my kernel speed to 25000 then, or 45000?

Mach shares time with Windows so the computer can do the necessary pulsing. 25000 is the most stable  because it provides the longest time period for the pulsing. Unless the required pulse rate exceeds what a Kernal speed can provide for, then there is no advantage to using something higher. When running Mach you should not have anything else running since whatever is running would be in competition for computer time. Additonal you want a nice flat straight line in the graph with no big spikes and the reported pulse rate to be very close to the kernel speed.

RICH